Surface layering

Surface layering is a quasi-crystalline structure at the surfaces of otherwise disordered liquids, where atoms or molecules of even the simplest liquid are stratified into well-defined layers parallel to the surface. While in crystalline solids such atomic layers can extend periodically throughout the entire dimension of a crystal, surface layering decays rapidly away from the surface and is limited to just a few near-surface region layers. Another difference between surface layering and crystalline structure is that atoms or molecules of surface-layered liquids are not ordered in-plane, while in crystalline solids they are. [C. A. Croxton, Liquid State Physics (Cambridge Univ. Press, Cambridge, England, 1974)]

Surface layering was predicted theoretically by Stuart Rice at the University of Chicago in 1983 [M. P. D’Evelyn and S. A. Rice, J. Chem. Phys. 78, 5081 (1983)] and has been experimentally discovered by Peter Pershan (Harvard) and his group, working in collaboration with Ben Ocko (Brookhaven) and Moshe Deutsch (Bar-Ilan) in 1995 in elemental liquid mercury [O. M. Magnussen, B. M. Ocko, M. J. Regan, K. Penanen, P. S. Pershan and M. Deutsch, "X-ray reflectivity measurements of surface layering in liquid mercury", Phys. Rev. Lett. 74, 4444 (1995).] and liquid gallium [M.J. Regan, et al., "Surface layering in liquid gallium: x-ray reflectivity study", Phys. Rev. Lett. 75, 2498 (1995).] using x-ray reflectivity techniques.

More recently layering has been shown to arise from electronic properties of metallic liquids, rather than thermodynamic variables such as surface tension, since surfaces of low-surface tension metallic liquids such as liquid potassium are layered [O. Shpyrko, P. Huber, A. Grigoriev, P. Pershan, B. Ocko, H. Tostmann, and M. Deutsch, Phys. Rev. B 67, 115405 (2003).] , while those of dielectric liquids such as water, are not [O. G. Shpyrko, M. Fukuto, P. S. Pershan, B. M. Ocko, T. Gog, I. Kuzmenko, “Suface Layering of Liquids: The Role of Surface Tension” Phys. Rev. B 2004, 69, 245423] .

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